diff --git a/src/Wolfgang.Etl.SqlBulkCopy/SqlBulkCopyLoader.cs b/src/Wolfgang.Etl.SqlBulkCopy/SqlBulkCopyLoader.cs
index be5a273..5fed3fb 100644
--- a/src/Wolfgang.Etl.SqlBulkCopy/SqlBulkCopyLoader.cs
+++ b/src/Wolfgang.Etl.SqlBulkCopy/SqlBulkCopyLoader.cs
@@ -61,6 +61,7 @@ public sealed class SqlBulkCopyLoader<TRecord> : LoaderBase<TRecord, SqlBulkCopy
     /// <exception cref="ArgumentNullException">
     /// Thrown when <paramref name="connection"/> is <c>null</c>.
     /// </exception>
+    [ExcludeFromCodeCoverage]
     public SqlBulkCopyLoader
     (
         SqlConnection connection
@@ -82,6 +83,7 @@ SqlConnection connection
     /// <exception cref="ArgumentNullException">
     /// Thrown when <paramref name="connection"/> or <paramref name="logger"/> is <c>null</c>.
     /// </exception>
+    [ExcludeFromCodeCoverage]
     public SqlBulkCopyLoader
     (
         SqlConnection connection,
@@ -106,6 +108,7 @@ ILogger<SqlBulkCopyLoader<TRecord>> logger
     /// <exception cref="ArgumentNullException">
     /// Thrown when <paramref name="connection"/> is <c>null</c>.
     /// </exception>
+    [ExcludeFromCodeCoverage]
     public SqlBulkCopyLoader
     (
         SqlConnection connection,
@@ -128,17 +131,18 @@ public SqlBulkCopyLoader
     /// </summary>
     /// <param name="wrapperFactory">The factory for creating bulk copy wrappers.</param>
     /// <param name="logger">An optional logger instance.</param>
-    /// <param name="timer">The progress timer to inject.</param>
+    /// <param name="timer">An optional progress timer to inject. When <c>null</c>, the
+    /// base class creates a <c>SystemProgressTimer</c>.</param>
     internal SqlBulkCopyLoader
     (
         ISqlBulkCopyWrapperFactory wrapperFactory,
         ILogger? logger,
-        IProgressTimer timer
+        IProgressTimer? timer
     )
     {
         _wrapperFactory = wrapperFactory ?? throw new ArgumentNullException(nameof(wrapperFactory));
         _logger = logger ?? NullLogger.Instance;
-        _progressTimer = timer ?? throw new ArgumentNullException(nameof(timer));
+        _progressTimer = timer;
         _options = SqlBulkCopyOptions.Default;
     }
 
@@ -657,6 +661,7 @@ private void EnsureConnectionAvailable(string operation)
 
 
 
+    [ExcludeFromCodeCoverage]
     private ISqlBulkCopyWrapperFactory CreateFactory()
     {
         EnsureConnectionAvailable("bulk copy");
diff --git a/tests/Wolfgang.Etl.SqlBulkCopy.Tests.Unit/SqlBulkCopyLoaderTests.cs b/tests/Wolfgang.Etl.SqlBulkCopy.Tests.Unit/SqlBulkCopyLoaderTests.cs
index 87241b9..ec9cc3c 100644
--- a/tests/Wolfgang.Etl.SqlBulkCopy.Tests.Unit/SqlBulkCopyLoaderTests.cs
+++ b/tests/Wolfgang.Etl.SqlBulkCopy.Tests.Unit/SqlBulkCopyLoaderTests.cs
@@ -559,6 +559,102 @@ public async Task LoadAsync_with_progress_reports_batch_count_Async()
 
 
 
+    // --- CreateProgressTimer fallback path test ---
+
+    [Fact]
+    public async Task LoadAsync_with_progress_when_no_timer_injected_uses_base_timer_Async()
+    {
+        var factory = new FakeSqlBulkCopyWrapperFactory();
+        var sut = new SqlBulkCopyLoader<TestRecord>(factory, logger: null, timer: null);
+        var captured = new List<SqlBulkCopyReport>();
+        var progress = new SynchronousProgress<SqlBulkCopyReport>(captured.Add);
+
+        await sut.LoadAsync(ToAsyncEnumerableAsync(CreateTestItems(3)), progress);
+
+        // The fact that LoadAsync completed without throwing means
+        // base.CreateProgressTimer(progress) was successfully invoked
+        // and the resulting SystemProgressTimer was started and stopped.
+        Assert.Equal(3, sut.CurrentItemCount);
+    }
+
+
+
+    // --- Invalid enum value tests ---
+
+    [Fact]
+    public Task LoadAsync_when_PreAction_is_invalid_enum_value_throws_Async()
+    {
+        var sut = CreateSut();
+        sut.PreAction = (PreAction)999;
+
+        return Assert.ThrowsAsync<ArgumentOutOfRangeException>
+        (
+            () => sut.LoadAsync(ToAsyncEnumerableAsync(CreateTestItems(1)))
+        );
+    }
+
+
+
+    [Fact]
+    public Task LoadAsync_when_PostAction_is_invalid_enum_value_throws_Async()
+    {
+        var sut = CreateSut();
+        sut.PostAction = (PostAction)999;
+
+        return Assert.ThrowsAsync<ArgumentOutOfRangeException>
+        (
+            () => sut.LoadAsync(ToAsyncEnumerableAsync(CreateTestItems(1)))
+        );
+    }
+
+
+
+    [Fact]
+    public async Task LoadAsync_when_PreAction_DeleteAllRecords_with_NotMapped_type_throws_Async()
+    {
+        var factory = new FakeSqlBulkCopyWrapperFactory();
+        var timer = new ManualProgressTimer();
+        var sut = new SqlBulkCopyLoader<NotMappedWithChildrenRecord>(factory, logger: null, timer)
+        {
+            PreAction = PreAction.DeleteAllRecords
+        };
+
+        var items = new[]
+        {
+            new NotMappedWithChildrenRecord { Id = 1 }
+        };
+
+        await Assert.ThrowsAsync<InvalidOperationException>
+        (
+            () => sut.LoadAsync(ToAsyncEnumerableAsync(items))
+        );
+    }
+
+
+
+    [Fact]
+    public async Task LoadAsync_when_PreAction_TruncateTable_with_NotMapped_type_throws_Async()
+    {
+        var factory = new FakeSqlBulkCopyWrapperFactory();
+        var timer = new ManualProgressTimer();
+        var sut = new SqlBulkCopyLoader<NotMappedWithChildrenRecord>(factory, logger: null, timer)
+        {
+            PreAction = PreAction.TruncateTable
+        };
+
+        var items = new[]
+        {
+            new NotMappedWithChildrenRecord { Id = 1 }
+        };
+
+        await Assert.ThrowsAsync<InvalidOperationException>
+        (
+            () => sut.LoadAsync(ToAsyncEnumerableAsync(items))
+        );
+    }
+
+
+
     // --- EnableDataValidation false path ---
 
     [Fact]